The printed circuit board (PCB) is a common component in modern electronic devices. PCBs hold (e.g., deploy, mount, support, etc.) integrated circuits (ICs) and other electronic devices, components, etc. PCBs comprise substantially planar, typically multi-layered boards that electrically interconnect the ICs, devices and components with conductive pathways (e.g., conductors, traces, etc.). Individual layers are bonded together to form a multi-layer PCB.
Their topologies and other attributes allow such PCBs to have conductive pathways on each of its several layers. Such multiplication of available conductive pathways promotes the ability of the PCBs to interconnect large numbers of such ICs and other devices, etc. and to support complex components (e.g., each having large numbers of integrated elementary components, etc.). This has benefits related to technical, economic, and/or other considerations.
Each PCB layer has a substantially planar base of an electrically insulating material, such as plastic, fiberglass, etc. The layer's conductive pathways are typically etched into a conductive material disposed upon a surface of that insulating base. Conductive pathways of each layer are insulated from those of adjacent layers with insulating bases. Conductive pathways of each layer are connectable with those of other layers with interlayer connections.
ICs and other devices are typically mounted on the surface of the PCB's outer layer by soldering their leads, traces, etc. into holes within the PCB. To use conductive pathways on other than the surface layer, the devices are electrically connected through these holes. Conventionally, such through-hole mounted devices, which they are sometimes called, are affixed and electrically connected using wave soldering and/or other soldering techniques.
Some through-hole mounted devices have significant size and weight. For instance, processors, and other devices may dissipate significant amounts of heat during their operation and may thus be mounted on the PCB with a heat sink of substantial relative weight. Power bricks and other devices can have substantial weight of their own, and may also be mounted on the PCB with a heavy heat sink, as well.
The weight of these devices and related inertial effects (e.g., in PCBs used in non-static installations) can stress the through-hole mounting. Heat they produce while operating can exacerbate negative effects related to this stress. Further, during operation, such devices may draw significant amounts of current, with related heat generating effects. Such currents determine the current carrying capacity characteristics, e.g., the ampacity, required for through-hole connections.
Such stresses and heating can adversely affect electrical characteristics including ampacity, and mechanical characteristics such as strength and brittleness of electromechanical connections. Such adverse effects can have unbeneficial consequences relating to capability, reliability, quality, etc. Conventional wave soldered through hole mounts can be subject to such adverse effects.
Further, challenges can be encountered in wave soldering large PCBs of several layers. For instance, for wave soldering (and other soldering techniques) to be effective for through hole mounting, the hole should be adequately and thoroughly heated, to allow molten solder to “wick” up into the hole to make a sound connection to a device lead therein. With differing thermal conductivities, localized heating, and other heating characteristics associated with various parts (e.g., depths within, etc.) of the hole however, this can be difficult to achieve. Conventional solutions such as thermal relief spokes are sometimes used. Notwithstanding however, thorough adequate heating of the hole can remain difficult to achieve and a complete solder fill may not be possible in some holes.
Conventionally, the problem of localized heating is sometimes addressed by removal of heat conducting components associated with a device to be mounted. For instance, relatively weighty devices such as power bricks and sizable heat sinks may be held in place on a PCB with mounting screws. The mounting screws however can effectively act as heat sinks during wave soldering, which can deter thorough adequate heating of the hole. To deter such localized heating during the wave soldering process, the mounting screws are sometimes removed, with some success.
This solution however poses other difficulties. For instance, after wave soldering the screw-mounted device with its mounting screws removed, the screws can not readily be replaced, because torquing the screws can mechanically stress the through-hole solder joint, possibly damaging or breaking it. Thus, the sole remaining mechanical support for the device after wave soldering is the through-hole solder joint just formed, which may only be partially filled. Stress from the device's weight and related inertial effects can adversely affect the mechanical strength, electrical integrity, and reliability of the solder joint, which may already be impacted by a less than thorough solder fill.
Further, wave-soldered through-hole mounts can be difficult or impossible to rework without damaging a PCB. Attempts to remove a device wave soldered to a PCB, e.g., for replacement, include de-soldering and a removing force, e.g., followed by re-soldering and an applying force. De-soldering and re-soldering heats the joint, e.g., to re-melt solder or allow molten solder to flow though the hole. Heat so added can be conducted to the device, to other devices, and into the insulating component of one or more layers and can cause damage. Mechanical stresses and strains associated with removing and installing the device can also cause damage.
Further, heating during wave soldering may not be uniform throughout the hole, which may thus be spanned by a significant temperature gradient. Such a significant temperature gradient can cause unequal cooling during solidification and crystallization of the solder. This can result in cracks and other deformities forming within the solder mass. Such defects can be especially troubling where the hole does not completely or adequately fill with solder. These defects can also adversely affect the electrical integrity of the solder joint. Thus reliability and quality can be impacted. Electrical and mechanical failures of solder joints have occurred, with resultant impact on the performance of the PCB.
Conventional approaches to the issues confronting wave soldering of large multi-layered (e.g., thick) PCBs include the Thermal Relief and Ampacity (THRAA) hole design. The THRAA hole design can achieve decent solder fill in holes of high layer count PCBs. However, the THRAA approach typically uses a manual process wherein each board is redesigned for incorporation. Numerous peripheral vias are typically needed, depending on the function of the PCB. It has been difficult to ascertain, prior to physical implementation, how many such vias are optimal for each hole. Further, reworking remains problematic even with the THRAA approach, because heating and mechanical stresses associated therewith still make damaging a PCB likely in rework.
One conventional approach to making connections on multi-layered PCBs uses a press-fit pin approach, e.g., to reduce dependency on solder as an electrical connection medium. Press-fit approaches apply a significant force to insert connection pins, and to extract them, e.g., in reworking the PCB. The forces used for insertion and extraction of the pins can be substantial. While the conventional press-fit pin approach can reduce dependency on solder, the substantial forces used therewith can damage conductive and insulating portions of various PCB layers and devices such as power bricks and neighboring devices and components and thus also render rework problematic. The potential for damage associated with this approach is too great for certain applications. Some other conventional approaches, such as the mill-max pin-in-socket design wherein a conductive socket is soldered into the PCB, prior to attachment of the pin, do not directly address the challenges posed by wave soldering.
Thus, conventional approaches to coupling electrical components can provide issues related to current carrying capability and concomitant heating effects, solderability, component removability, replacability and reworkability and/or mechanical supportability. Moreover, some techniques developed in response to these issues can provide issues of their own, some of which relate to the potential of such techniques causing resizing (e.g., of holes and proximate PCB material), wear and/or damage of the PCBs and/or the electrical components.